Suspending and Resuming Auto Scaling Processes

Auto Scaling enables you to suspend and then resume one or more of the Auto Scaling processes
in your Auto Scaling group. This can be very useful when you want to investigate a configuration
problem or other issue with your web application and then make changes to your application,
without triggering the Auto Scaling process.

Auto Scaling might suspend processes for Auto Scaling groups that repeatedly fail to launch instances.
This is known as an administrative suspension, and most
commonly applies to Auto Scaling groups that have been trying to launch instances for over
24 hours but have not succeeded in launching any instances.
You can resume processes suspended for administrative reasons.

Auto Scaling Processes

If you suspend Launch, this disrupts other processes.
For example, you can't return an instance in a standby state to service
if the Launch process is suspended, because the group can't
scale.

Terminate

Removes an EC2 instance from the group, decreasing its capacity.

Warning

If you suspend Terminate, this disrupts other processes.

HealthCheck

Checks the health of the instances. Auto Scaling marks an instance as unhealthy if Amazon EC2
or Elastic Load Balancing tells Auto Scaling that the instance is unhealthy. This process can override
the health status of an instance that you set manually.

ReplaceUnhealthy

Terminates instances that are marked as unhealthy and subsequently creates new instances to replace
them. This process works with the HealthCheck process, and uses both the
Terminate and Launch processes.

AZRebalance

Balances the number of EC2 instances in the group across the Availability Zones in the region.
If you remove an Availability Zone from your Auto Scaling group or an Availability Zone otherwise becomes unhealthy
or unavailable, Auto Scaling launches new instances in an unaffected Availability Zone before terminating the
unhealthy or unavailable instances. When the unhealthy Availability Zone returns to a healthy state,
Auto Scaling automatically redistributes the instances evenly across the Availability Zones for the group.

Note that if you suspend AZRebalance and a scale out or scale in event occurs, Auto Scaling still
tries to balance the Availability Zones. For example, during scale out, Auto Scaling launches the instance
in the Availability Zone with the fewest instances.

If you suspend Launch, AZRebalance neither launches new instances nor
terminates existing instances. This is because AZRebalance terminates instances only
after launching the replacement instances. If you suspend Terminate, your Auto Scaling group can
grow up to ten percent larger than its maximum size, because Auto Scaling allows this temporarily during
rebalancing activities. If Auto Scaling cannot terminate instances, your Auto Scaling group could remain above
its maximum size until you resume the Terminate process.

AlarmNotification

Accepts notifications from CloudWatch alarms that are associated with the group.

If you suspend AlarmNotification, Auto Scaling does not
automatically execute policies that would be triggered by an alarm. If
you suspend Launch or Terminate, Auto Scaling would
not be able to execute scale out or scale in policies,
respectively.

ScheduledActions

Performs scheduled actions that you create.

If you suspend Launch or Terminate, scheduled actions that
involve launching or terminating instances are affected.

AddToLoadBalancer

Adds instances to the attached load balancer or target group when they are launched.

If you suspend AddToLoadBalancer, Auto Scaling launches the instances but
does not add them to the load balancer or target group. If you resume the AddToLoadBalancer
process, Auto Scaling resumes adding instances to the load balancer or target group when they are launched.
However, Auto Scaling does not add the instances that were launched while this process was
suspended. You must register those instances manually.

Suspend and Resume Processes Using the Console

You can suspend and resume individual processes using the AWS Management Console.